Eager
Transform stored data before the new schema becomes authoritative.
Migrations
Describe the meaning of a change before moving data
A migration connects immutable schema versions with an explicit mapping. Its physical strategy can then be eager, lazy, or virtual.
Migration timeline
Separate semantic change from physical work
The schema version and mapping define meaning. Eager, lazy, and virtual modes describe distinct physical execution choices.
DeclareMeaning
EagerExecution mode
LazyExecution mode
VirtualExecution mode
MeaningSemantic change
Create an immutable schema version and a typed mapping. This changes the semantic model; it does not by itself claim that physical data moved.
Static explanation
- Semantic change. Create an immutable schema version and a typed mapping. This changes the semantic model; it does not by itself claim that physical data moved.
- Eager physical execution. Move or rewrite physical data before cutover, then switch readers to the new schema version.
- Lazy physical execution. Defer record conversion until data is read, while preserving the declared version boundary.
- Virtual execution. Interpret the mapping at query time without eagerly copying the source records.
Three physical modes
Lazy
Transform records when they are read or rewritten.
Virtual
Keep storage unchanged and expose a compatibility view.
Cost and coordination remain
Typed mappings can make a migration easier to validate and compose. They do not remove downtime, information loss, rewrite cost, or the need to coordinate noncommutative changes.